Robust carbon monolith having hierarchical porosity

ABSTRACT

A carbon monolith includes a robust carbon monolith characterized by a skeleton size of at least 100 nm, and a hierarchical pore structure having macropores and mesopores.

The United States Government has rights in this invention pursuant tocontract no. DE-AC05-00OR22725 between the United States Department ofEnergy and UT-Battelle, LLC.

FIELD OF THE INVENTION

The present invention relates to carbon monoliths having hierarchicalporosity, and more particularly to robust carbon monoliths characterizedby macropores and mesopores.

BACKGROUND OF THE INVENTION

The invention addresses two different and independent difficulties inthe art of liquid chromatography.

Firstly, there is a lack of robust stationary phases for highperformance liquid chromatography (HPLC) that provide broadly usefulretention and separation patterns. Benefiting from the superiorhydraulic and mass transfer kinetic properties of a monolithicstructure, a variety of monolithic columns have been developed for fastseparations during the last few years. These well known monolithiccolumns are categorized in to two general groups: silica-based columnsand polymeric columns. Silica-based stationary phases are generallyfeasible only with mobile phases having a pH in the range of 3 to 10.Moreover, although polymeric phases are not as pH-limited, they areoften degraded rapidly when used with certain common organic solventsand/or at high temperatures. Thus, there is a need for a ruggedmonolithic column made with a stationary phase that can be used in awide range of chemical environments and at elevated temperatures.

Electrochemically modulated liquid chromatography (EMLC) requires anelectrically conductive stationary phase, which generally excludes allsilica-based and most polymeric stationary phases. Carbon-basedparticulate stationary phases are currently the only type of stationaryphases used for EMLC. Conventional beds packed with porous graphiteparticles suffer from a poor electrical conductivity, hence from aheterogeneous distribution of the electric charges of the particles. Theelectrical equilibrium of the column can only be achieved after washingit for a very long time with the mobile phase. This causes a slowadjustment of the experimental conditions and the waste of valuablechemicals. The development of EMLC has been considerably slowed down bythe lack of a suitable stationary phase.

Carbon monoliths having hierarchical porosity have been made using asilica monolith having hierarchical porosity as a template. Carbonmonoliths made thereby take the shape of the voids (pores) of thetemplate and are of very low density and are not structurally robust.Such carbon monoliths are known to undergo structural collapse under anelectron beam of an electron microscope. A robust carbon monolith havinghierarchical porosity is needed for applications such as chromatographyand other chemical separations.

OBJECTS OF THE INVENTION

Accordingly, objects of the present invention include provision of: arobust carbon monolith having hierarchical porosity; a robust carbonmonolith characterized by macropores and mesopores; a monolithic columnfor HPLC that can be used in a wide range of chemical environments andat elevated temperatures; a highly conductive monolithic column forHPLC; a method of synthesis of a porous carbon monolith; use of any ofthe foregoing as a versatile HPLC column bed; use of any of theforegoing as a highly conductive EMLC column; and a robust material thatis characterized by a combination of chemical merits of a high specificsurface area carbon adsorbent and superior hydrodynamic properties of amonolithic structure. Further and other objects of the present inventionwill become apparent from the description contained herein.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, the foregoingand other objects are achieved by a carbon monolith that includes arobust carbon monolith characterized by a skeleton size of at least 100nm, and a hierarchical pore structure having macropores and mesopores.

In accordance with another aspect of the present invention, a monolithicchromatography column includes a robust monolithic carbon stationaryphase disposed in a chromatography column, the monolithic carbonstationary phase characterized by a skeleton size of at least 100 nm.

In accordance with another aspect of the present invention, a method ofpreparing a robust carbon monolith includes the steps of: providing acarbon monolith precursor having a porosity-generating fugitive phasedispersed therein, the fugitive phase comprising mesoparticles andmicroparticles; carbonizing the carbon monolith precursor to form acarbon monolith: and removing the fugitive phase from the carbonmonolith to form a robust, porous carbon monolith characterized by askeleton size of at least 100 nm, and a hierarchical pore structurehaving macropores and mesopores.

In accordance with another aspect of the present invention, a method ofpreparing a robust carbon monolith includes the steps of: providing acarbon monolith precursor having a particulate porosity-generatingfugitive phase dispersed therein, the fugitive phase comprisingmesoparticles and microparticles; and heating the carbon monolithprecursor to carbonize the carbon monolith precursor, and to remove thefugitive phase from the carbon monolith, to form a robust, porous carbonmonolith characterized by a skeleton size of at least 100 nm, and ahierarchical pore structure having macropores and mesopores.

In accordance with another aspect of the present invention, a method ofpreparing a monolithic chromatography column includes the steps of:providing a carbon monolith precursor having a porosity-generatingfugitive phase dispersed therein; carbonizing the carbon monolithprecursor to form a carbon monolith; removing the fugitive phase fromthe carbon monolith to form a robust, porous carbon monolithcharacterized by a skeleton size of at least 100 nm, and a hierarchicalpore structure having macropores and mesopores; and encapsulating theporous carbon monolith to form a chromatographic column.

In accordance with another aspect of the present invention, a method ofpreparing a monolithic chromatography column includes the steps of:providing a carbon monolith precursor having a porosity-generatingfugitive phase dispersed therein; heating the carbon monolith precursorto carbonize the carbon monolith precursor to form a carbon monolith,and to remove the fugitive phase from the carbon monolith; and

-   -   encapsulating the porous carbon monolith to form a        chromatographic column.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the three-dimensional molecularstructure of the resorcinol iron (III) complex.

FIG. 2 is a schematic illustration of the co-polymerization offormaldehyde and resorcinol iron (III) complex.

FIG. 3 is a schematic illustration of a carbon precursor tailored bycolloidal spheres in accordance with the present invention.

FIG. 4 is a schematic illustration showing the principle of reactioninduced phase separation of a ternary system in accordance with thepresent invention.

FIG. 5 is a photomicrograph showing the macropore morphology of a carbonmonolith made by disordered colloidal templates in accordance with thepresent invention.

FIG. 6 is a photomicrograph showing the morphology of a carbon monolithmade by ordered colloidal array in accordance with the presentinvention.

FIG. 7 is a photomicrograph showing the secondary porosity of a carbonmonolith made by colloidal templates in accordance with the presentinvention.

FIG. 8 is a photomicrograph showing the morphology of a carbon monolithwhich has 800 nm macropores with the skeleton size of 250 nm inaccordance with the present invention.

FIG. 9 is a photomicrograph showing the sample has 1.5 μm macropores inaccordance with the present invention.

FIG. 10 is a photomicrograph showing a carbon sample with 2 μmmacropores in accordance with the present invention.

FIG. 11 is a photomicrograph showing a carbon sample with 3 μmmacropores in accordance with the present invention.

FIG. 12 is a photomicrograph showing a carbon sample with 5 μmmacropores in accordance with the present invention.

FIG. 13 is a photomicrograph showing a carbon sample with approximate 10μm macropores in accordance with the present invention.

FIG. 14 is a photomicrograph showing a carbon sample with approximate 20μm macropores in accordance with the present invention.

FIG. 15 is a photomicrograph showing the secondary porosity of a carbonmonolith in accordance with the present invention.

FIG. 16 is a TEM image of the mesopores on a carbon monolith inaccordance with the present invention.

FIG. 17 a is a schematic illustration showing a radial cross-section ofa carbon column in accordance with the present invention.

FIG. 17 b is a schematic illustration showing an axial cross-section ofa carbon column in accordance with the present invention.

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above-described drawings.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, a robust, hierarchicallyporous carbon monolith is characterized by a combination of:

-   1. Macropores having a size in the range of 0.05 μm to 100 μm,    preferably in the range of 0.1 μm to 50 μm, more preferably in the    range of 0.8 μm to 10 μm;-   2. Mesopores having a size range of 18 Å to 50 nm, preferably in the    range of 0.5 nm to 40 nm, more preferably in the range of 5 nm to 30    nm; and-   3. A skeleton size (monolith wall thickness) in the range of 100 nm    to 20 μm, preferably in the range of 200 nm to 10 μm, more    preferably in the range of 400 nm to 1 μm.

Graphitized carbon can serve as a highly inert stationary phase that canbe used under harsh experimental conditions, e.g., with an extremelyacidic or basic solution as the mobile phase in HPLC applications. Therobust monolithic structure permits the achievement of a highpermeability and fast mass transfer kinetics. Moreover, the column has alow backpressure and fast HPLC separations can be performed. Someadvantages of a carbon monolithic liquid chromatography column include:a combination of the chemical merits of a high specific surface areacarbon adsorbent and a superior hydrodynamic properties of a monolithicstructure.

Another unique feature of a carbon monolithic column is its excellentelectrical conductivity. It is possible to modulate retention byadjusting the potential of the carbon surface. Thus, a carbon monolithiccolumn is ideal for EMLC because the high electrical conductivity allowsa homogeneous surface potential over the entire column and a rapidequilibrium after changes of the applied external electric field.

The present invention provides new liquid chromatography separationpatterns, profoundly different from those achieved with known stationaryphase materials.

The present invention provides methods of fabricating of a wide varietyof carbon monoliths that are especially useful as columns for HPLCand/or EMLC applications. Appropriate modifications to thecharacteristics of materials used in fabricating the columns allow theachievement of various trade-offs in column efficiency, permeability,rate of separation, column loading capacity, etc. The column is made ofa hierarchically porous carbon monolith, which is preferably first cladwith a heat shrinkable tube and then encapsulated in a metal orpolyether-ether-ketone (PEEK) tube. A carbon monolith, or “skeleton” ischaracterized by macropores and mesopores (secondary porosity). Thesecondary porosity contributes to the surface area which is required toachieve the desired separation. Such a hierarchical structure enablesfast separation with superior hydraulic properties.

A robust monolith skeleton wall thickness must be at least 100 nm andmay be as large as 20 μm. The generally accepted optimal wall thicknessfor HPLC applications is from 200 nm to 5 μm. HPLC applications inparticular require column material that can sustain pressure from 10bars to 400 bars. Carbon monolithic material of the present invention issurprisingly robust, and can withstand sustains pressure up to 400 barswithout undergoing any structural damage or collapse.

Fabrication of a robust carbon monolithic column in accordance with thepresent invention includes the following general steps: preparation of acarbon monolith precursor having a porosity-generating fugitive phase;carbonization of the precursor and the removal of the fugitive phase;optional graphitization; and encapsulation to form a chromatographiccolumn.

Preparation of Precursor

A carbon monolith precursor is defined as any material that can becarbonized to form a carbon monolith that can be used for achromatographic separation. The precursor must include a particulate,porosity-generating, fugitive phase which serves as a template for thepores that characterize the final product. A carbon monolith precursoris prepared in any desired shape, but is usually rod-shaped to conformto the general shape and size of a liquid chromatography column.Precursors can be prepared by several methods in accordance with thepresent invention; several examples are described hereinbelow.

Method 1: Fe Catalyzed Polymer with a Template of Silica Beads

Step 1: Silica beads sized from 800 nm to 10 μm are dispersed in asolvent in a concentration range of 0.1 to 2 g/g using an appropriatedispersing method such as ultrasonic mixing, for example, to form acolloid. The solvent can be any polar solvent or solvent mixture. Amixture of ethanol and water is suggested.

Step 2: FeCl₃ is dissolved into the colloid in a concentration range of0.001 to 0.5 g/g.

Step 3. Resorcinol is dissolved into the colloid in a concentrationrange of 0.1 to 2.5 g/g.

Step 4. The colloid is agitated to facilitate a reaction to form aresorcinol/Fe(III) complex, illustrated in FIG. 1.

Step 5. A 5% to 37% solution of formaldehyde in water is cooled to atemperature in the range of about 0° C. to 20° C. and added to thecolloid in a concentration range of 0.01 to 2.5 g/g.

Step 6. The colloid is cooled to a temperature in the range of about 0°C. to 20° C. and stirred for a time period of 5 min to 30 min to effecthomogeneousness.

Step 7. The colloid is transferred into a mold of desired monolith shapeand heated to a temperature in the range of about 50° C. to 95° C. for atime period of 0.5 h to 20 h to effect polymerization of the colloidinto a solid monolith, shrinkage of the monolith from the mold wall, andcuring of the monolith. FIG. 2 shows the polymerization reaction.

Step 8. The solid monolith is removed from the mold and the solvent isevaporated therefrom to dryness.

Step 9. The dry monolith is cured at a temperature in the range of about40° C. to 150° C. for a time period of 3 h to 20 h to effect completepolymerization of the monolith material.

EXAMPLE I

6 g of silica beads were dispersed in 5 g of an aqueous solution ofethanol (80% ethanol, 20% water) using an ultrasonic mixer. 1.08 g FeCl₃was then dissolved into the suspension, followed with 2.2 g ofresorcinol, dissolved by hand shaking. The colloid solution turned darkimmediately after the addition of resorcinol, indicating the formationof a resorcinol/Fe(III) complex. 2.4 g of an ice-cooled, 37%formaldehyde solution in water was introduced into this mixture, in onestep, with hand shaking. The mixture was kept in an ice-water bath for10 minutes with magnetic stirring. After removal of the ice-water bath,the mixture was slowly transferred into 5 mm ID glass tubes which werecapped when filled. These tubes were then placed in a 70° C. water bath.The mixture polymerized rapidly into a solid rod inside the glass tube.This rod detached from the tube wall because of the shrinking caused bypolymerization. The polymer rod was aged time period of 5 h in the glasstube, which was kept in the hot-water bath. The crack-free phenolicresin/silica rods were removed from the glass tubes by shaking each tubetoward its open end. The wet rod was put into the hood for three days,in order to evaporate the solvent. Finally, it was thoroughly dried in avacuum oven at 80° C., time period of 10 h. The dried rods were furthercured at 135° C. for 4 h to ensure complete polymerization.

Method 2: Fe Catalyzed Polymer with a Template of Polystyrene Beads

This method is essentially the same as Method 1 above, the onlydifference being that polystyrene beads replace the silica beads.

Method 3 Fe Catalyzed Polymer with a Duplex Template of Silica Beads

This method is also similar to Method 1, but a suspension of silicabeads of two discrete, different particle sizes is used. The largerparticles can generally be in a size range of 800 nm to 10 μm, thesmaller particles can generally be in a size range of 6 nm to 100 nm,and the population ratio of the larger particles to smaller particlescan generally be in a range of 0.1 to 10.

After Step 6 as described above, the colloid is subject tocentrifugation at a sufficient RPM and for a sufficient period of timeto effect formation of large particles into a compacted orderedmacroporous colloidal array while the small particles remain as a stablesuspension in the interstices of the array. The porosities of themacropore and mesopore arrays can be finely adjusted by varying theratio of the differently sized particles.

EXAMPLE II

Generally following the method of Example I, 2 g of silica beads havinga particle size of 5 μm and 1 g of silica beads having a particle sizeof 13 nm were used. Following introduction of the formaldehyde solution,the colloid was centrifuged at about 3000 RPM for 30 min. Only the largeparticles form a compacted ordered colloidal array while the smallparticles remain as a stable suspension between them. After removal ofthe supernant, poly-condensation of the colloidal array into a rod wascarried out in the centrifuge tube in an oven at 50° C.

Method 4: Fe Catalyzed Polymer with a Duplex Template of PolystyreneBeads

This method is essentially the same as Method 3 above, the onlydifference being that polystyrene beads replace the silica beads.

For a better understanding of the above described colloidal templatingmethods, FIG. 3 illustrates the fabrication of the precursor monolithsmade via methods 1 to 4. The colloidal array 30 can be silica and/orpolystyrene spheres 32. The voids 34 are filled with carbon precursor.As will be described hereinbelow, silica spheres are removed by HF orNaOH after carbonization, and polystyrene spheres are removed by thermaldecomposition during carbonization, leaving a carbon skeleton.

Method 5: Double Condensation Method

An ethanol solution of tetraethoxylsilane (TEOS) in a concentration of0.1 to 5 g/g, polyethylene-oxide-propylene-oxide-ethylene-oxide (P123)in a concentration of 0.1 to 5 g/g, and 1M HCl in a concentration of0.0001 to 0.04 g/g is prepared. The mixture is cast into a tube andgelled into a monolith at a temperature in the range of about 30° C. to80° C. for a time period in the range of about 2 h to 10 h. The monolithis then dried at a temperature in the range of about 50° C. to 150° C.,preferably in a vacuum oven.

EXAMPLE III

10.4 g of TEOS, 8.7 g P123 and 3.5 g 1 m HCl were mixed in 69 g ethanol.The mixture reacted at 70° C. for 1.5 h. 3.3 g resorcinol in 3.6 g 37%formaldehyde was added into the mixture after the removal of ethanol byvacuum. The final mixture was introduced into a glass tube and reactedat 80° C. for 4 h. Afterwards the rod was thoroughly dried in a vacuumoven at 100° C.

Method 6: Reaction Induced Dual Phase Separation of Ternary OrganicMixture

A homogeneous solution of component A, component B, and component C isinduced to perform dual phase separation via reaction. Thepolymerization of component A induces a primary phase separation ofpolymerized component A and component C in micron or submicron scale. Ascomponent A polymerizes, component B becomes enriched in the polymerizedphase of component A. With further polymerization of component A,component B separates from component A, resulting in a secondary,nanometer scale phase separation. The removal of components B and Cyields the desired hierarchical porous structure of the carbon precursorneeded to carry out the present invention. FIG. 4 shows schematicallythe principle of the polymerization induced phase separation the ternarysystem.

In this system, component A is carbon forming agent, component B is amesopore forming agent, and component C is a macropore forming agent.The three components are mixed together, transferred into a mold ofdesired monolith shape, allowed to settle for a time period of 2 h to 20h and heated to a temperature in the range of about 40° C. to 50° C. fora time period of 1 h to 72 h to effect curing of the monolith. Themonolith is then hardened by treating with 20% to 80% sulfuric acid fora time period of 2 h to 10 h. Components B and C are then removed bywashing the monolith, for example, with copious water. The monolith canthen be thoroughly dried. Drying method is not critical, but it issuitable to dry the monolith in a vacuum oven at nominal 100° C.

Component A is generally comprised of at least one monomer, and can beselected from at least the following examples: furfuryl alcohol, alkylsubstituted furfuryl alcohol, furfuryl aldehyde, alkyl substitutedfurfuryl alcohol, phenol, alkyl phenol, phenolic alcohol, and alkylsubstituted phenolic alcohol, epoxy, and polymers of the aforementionedcompositions.

Component B can be comprised of at least one surfactant and/or alow-charring polymer. Nearly all surfactants, including ionicsurfactants and nonionic surfactants are contemplated as suitable foruse as component B. Polyethylene oxides of various molecular weights,generally in the range of 200 to 100000 Dalton, are suitable candidatesfor component B.

Oligomer C can be selected from at least the following examples:ethylene glycol, diethylene glycol, triehtylene glycol, tetraenthyleneglycol, poly ethylene glycol, oleic acid, propylene glycol, dipropyleneglycol, and water.

Polymerization catalysts, crosslinkers, and/or curing agents can beadded to the mixture.

EXAMPLE IV

Two solutions were made separately. 4 g of p-toluenesulforic acidmonohydrate dissolved in 46 g of diethylene glycol. 25 g of surfactantP123 dissolved in 25 g of furfuryl alcohol. These two solutions werethen mixed with mechanic stirring at room temperature. This mixture wasthem cast into a cylindrical model of appropriate diameter and settle atroom temperature for a time period of 12 h before final curing at 70° C.for 24 h. The cured mixture formed an organic polymer rod withinterconnected macropores which filled with the macropore forming agent.The rod was hardened by treating the rod with 60% sulfuric acid at 80°C. for a time period of 2 h. The surfactant and the macropore formingagents were then removed by washing the rod with copious water. The rodwas thoroughly dried in a vacuum oven at 100° C.

Carbonization, Removal of Fugitive Phase, and Graphitization

Precursors made as described above can be carbonized by any conventionalcarbonization method. Carbonization can generally comprise heating in aninert environment. The particular method is not critical to theinvention, although some methods will be found to be better than others,depending on the desired result.

Following carbonization, soluble fugitive phases and catalysts areremoved by dissolution with a solvent that does not harm the carbonizedmonolith. Thermally decomposable and or volatile fugitive phases aregenerally removed during carbonization and/or graphitization.

Carbonized monoliths can then be graphitized by any conventionalgraphitization method. Graphitization can generally comprise heating inan inert environment to a temperature exceeding the carbonizationtemperature. The particular method is not critical to the invention,although some methods will be found to be better than others, dependingon the desired result. Graphitization is preferred because itessentially eliminates microporosity (pores <18 Å), but anon-graphitized carbon monolith can be used for some applications.Microporosity can be also blocked by known chemical modificationmethods.

Carbonization of precursor monoliths made by Methods 1, 3, and 5described above is followed by the removal of silica template and/orcatalyst, which is followed by graphitization. FIGS. 5 to 7 show themorphologies of carbon monoliths made via colloidal templates.

EXAMPLE VI

Precursor rods which were made by Methods 1, 3, and 5 described abovewere placed into a cylindrical furnace, purged with N2 (45 ml/min). Aprogrammed temperature cycle was applied to the furnace. The temperaturewas first ramped from 135 to 800° C. at 2.5° C./min and then keptconstant at 800° C. for 2 h, to ensure complete carbonization. A secondtemperature ramp took place from 800° C. to 1250° C. at 10° C./min. Thetemperature was kept constant at 1250° C. for 1 h. Afterward, thefurnace was allowed to cool naturally to ambient temperature. The silicabeads and the iron catalyst were removed by washing with a concentratedsolution of hydrofluoric acid followed by rinsing with copious amountsof distillated water. The porous carbon rod obtained was thoroughlydried under vacuum at 80° C.

EXAMPLE VII

Porous carbon rods made in accordance with Example VI were graphitizedby high temperature treatment (HTT). The temperature ramps wereprogrammed as a slow ramp from room temperature to 1600° C. at the rateof 5° C./min, and then followed by a rapid ramp to 2400° C. at the rateof 10 to 20° C./min. The temperature was kept at 2400° C. for 10 to 30minutes then cooled down to ambient temperature.

The pore forming agents used in Methods 2, 4, and 6 are thermallydecomposable and/or volatile. Following carbonization, the carbonmonolith does not generally contain any other elements except carbon.Therefore, a single process can be used to carbonize the precursor,remove the fugitive phase (generally via decomposition and/orvolatilization), and graphitize the carbon monolith. The precursor madevia method 6 is carbonized and graphitized by heating, preferably in acontrolled fashion, from room temperature to graphitization temperaturewhich is in the range of 2100° C. to 2800° C.

EXAMPLE VIII

Precursor rods prepared by Methods 2, 4, and 6 described above werecarbonized and graphitized through a programmed continuous temperatureprocedure. A slow temperature ramp at the rate of 0.1 to 1° C./min wasapplied from room temperature to 750° C. to carbonize the polymer rodsand followed by a fast temperature ramp at the rate of 2 to 20° C./minto the 2400° C./min and hold at 2400° C. for half an h to graphitize thecarbonized rods.

By varying the pore forming agents the sizes of the macropores andmesopores can be finely adjusted within the limits set forthhereinabove. FIGS. 8 to 14 show morphologies of macropores with varioussizes. These macropores are the primary porosity of the carbonmonoliths. A secondary phase separation results in the secondaryporosity on the carbon skeleton. FIG. 15 shows the secondary porosity onthe carbon skeleton. FIG. 16 shows the mesopores examined bytransmission electron microscopy (TEM).

Cladding of Graphitized Monolith

Following graphitization, the robust carbon monolith is fabricated intoa column for liquid chromatography in accordance with the presentinvention. FIGS. 17 a, 17 b schematically illustrate the cross-sectionof a carbon column 70. First, the monolith 72 can be clad with an inertcladding 74, such as polytetrafluoroethylene (PTFE).

Fabrication of Chromatography Column

The clad monolith is subsequently coated with a cementing agent such asepoxy cement, and inserted into a structurally robust tube that issuitable for use as a liquid chromatography column. Typical tubes are ¼″stainless steel tubing, cut to typical or desired length. After thecement cures, the column is complete and ready to be connected to aliquid chromatography system, generally using reduction unions. Avariety of different columns can be made by using carbon monoliths ofdifferent diameters and lengths. The dimension of the column can thus bevaried due to the requirements of applications.

EXAMPLE IX

The carbon rod was clad in an oven at 340° C. with a section ofheat-shrinkable Teflon tubing. The encapsulated carbon rod was thencemented into a precut stainless steel tube, with epoxy cement.

Various cladding materials may be used to encapsulate the porous carbonmonolith in accordance with the present invention. The claddingmaterials can be thin tubes made of, for example, heat-shrinkable PTFE,PEEK, fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), ormixtures of these polymers. They are available in all necessary sizesand grades. Some are resistant to the same chemicals as the carbonmonoliths. When the carbon monolith is encapsulated with a section ofheavy-duty-walled heat-shrinkable tube, the end fits can be directlyattached to the column without the shield of steel tube. For example,when the carbon monolith is clad with a section of thick wall heatshrinkable PEEK tube, end fitting nuts can be directly machined on thecolumn.

FIGS. 17 a, 17 b show schematically, not to scale, a chromatographycolumn 70 including carbon monolith 72, cladding 74, and tube 76.

The monolithic carbon column can be made into any dimensions with anydesired shape and dimensions in accordance with the present invention.Examples of contemplated shapes include, but are not limited to rod,disk, tube, annular, angular, helical, coil, etc.

The monolithic carbon column can be subject to chemical treatment of thecarbon monolith with functionalities for the enhancement of theseparation effect. Examples of chemical treatment include, but are notlimited to: chemically oxidizing the carbon surface; chemically graftingligands and/or organic chains to the carbon surface; electrochemicallyreducing aryl diazonium salts on the carbon surface; electrochemicallyoxidizing alkylamines on the carbon surface; electrochemically oxidizingarylacetates on the carbon surface; and electrochemically oxidizingalcohols on the carbon surface.

Moreover, the monolithic carbon column can be subject to physicaltreatment of the carbon monolith with functionalities for theenhancement of the separation effect. Examples of physical treatmentinclude, but are not limited to physical absorption of functionalmolecules such as surfactants, macromolecules, crown ether, porphyrin,and other compositions that are generally used for the purpose ofenhancing chromatographic separations.

The monolithic carbon column can be used as sorbents for solid phaseextraction processes.

The monolithic carbon column can be used for gas chromatography and anyother type of analytical chromatographic separation.

The monolithic carbon column can be used as catalyst bed. For example,catalyst particles can be chemically or electrochemically deposited inthe pores of the carbon monolithic column. Various catalyst particlescan be used to catalyze various reactions.

The monolithic carbon column can be used as porous electrode for anyelectrochemical system, especially those that require high electrodesurface area. The carbon monolithic column can also be used as aflow-through electrode for continuous electrochemical processes.

The present invention is generally characterized by at least threeadvantages in liquid chromatography applications:

1) Carbon monolithic columns made in accordance with the presentinvention have an extremely high resistance to aggressive chemicals.They can be used with solutions having any pH (from below 0 to above 14,if needed), with nearly any solvent or solvent mixtures, and at anypractical temperature. The carbon monolithic columns can generally beattacked only by concentrated hydrogen peroxide, solutions of organicperoxides and of ozone, and are free from many of the disadvantages ofsilica- or polymer-based columns.

2) Benefiting from the monolithic structure, carbon monolithic columnsexhibit a much lower back pressure than columns packed with smallparticles. This makes the present invention most suited for fastseparations.

3) Carbon monolithic columns made in accordance with the presentinvention exhibit a high electrical conductivity and are electricallyhomogeneous. This makes them ideal for EMLC.

The present invention can be, among other applications, used as theworking electrode of EMLC columns. The column may be configured as a2-electrode or a 3-electrode EMLC column. According to the requirementsof the analyst, the counter-electrode and of the reference electrodecould be placed in the column, upstream, or downstream of the column.

While there has been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications can beprepared therein without departing from the scope of the inventionsdefined by the appended claims.

1. A method of preparing a robust carbon monolith comprising the stepsof: a. providing a colloidal solution comprising a carbon monolithprecursor having a porosity-generating fugitive phase dispersed therein,said fugitive phase comprising a low-charring polymer andmicroparticles; b. carbonizing said carbon monolith precursor to form acarbon monolith: and c. removing said fugitive phase from said carbonmonolith to form a robust, porous carbon monolith characterized by askeleton size of at least 100 nm, and a hierarchical pore structurehaving macropores and mesopores, wherein removal of the low-charringpolymer provides the mesopores.
 2. A method in accordance with claim 1wherein said carbon monolith precursor further comprises at least onecarbonizable polymer.
 3. A method in accordance with claim 1 whereinsaid porosity-generating fugitive further comprises a material that issoluble in a solvent that does not harm said porous carbon monolith. 4.A method in accordance with claim 1 wherein said porosity-generatingfugitive further comprises silica.
 5. A method in accordance with claim1 further comprising, after said removing step, an additional step ofgraphitizing said porous carbon monolith.
 6. A method in accordance withclaim 1 wherein said carbon monolith is characterized by a skeleton sizeof 100 nm to 20 μm.
 7. A method in accordance with claim 6 wherein saidcarbon monolith is characterized by a skeleton size of 200 nm to 10 μm.8. A method in accordance with claim 7 wherein said carbon monolith ischaracterized by a skeleton size of 400 nm to 1 μm.
 9. A method inaccordance with claim 1 wherein said macropores are of a size range of0.05 μm to 100 μm.
 10. A method in accordance with claim 9 wherein saidmacropores are of a size range of 0.1 μm to 50 μm.
 11. A method inaccordance with claim 10 wherein said macropores are of a size range of0.8 μm to 10 μm.
 12. A method in accordance with claim 1 wherein saidmesopores are of a size range of 5 nm to 30 nm.
 13. A method ofpreparing a robust carbon monolith comprising the steps of: a. providinga colloidal solution comprising a carbon monolith precursor having aparticulate porosity-generating fugitive phase dispersed therein, saidfugitive phase comprising mesoparticles and microparticles; and b.heating said carbon monolith precursor to carbonize said carbon monolithprecursor, and to remove said fugitive phase from said carbon monolith,to form a robust, porous carbon monolith characterized by a skeletonsize of at least 100 nm, wherein removal of said fugitive phasecomprising mesoparticles and microparticles provides a hierarchical porestructure having macropores and mesopores.
 14. A method in accordancewith claim 13 wherein said carbon monolith precursor further comprisesat least one carbonizable polymer.
 15. A method in accordance with claim13 wherein said porosity-generating fugitive phase further comprises amaterial that is thermally removable at a temperature that does notdecompose said porous carbon monolith.
 16. A method in accordance withclaim 13 wherein said porosity-generating fugitive phase furthercomprises at least one material selected from the group consisting ofsurfactants and low-charring polymers.
 17. A method in accordance withclaim 13 further comprising, after said removing step, an additionalstep of graphitizing said porous carbon monolith.
 18. A method inaccordance with claim 13 wherein said carbon monolith is characterizedby a skeleton size of 100 nm to 20 μm.
 19. A method in accordance withclaim 18 wherein said carbon monolith is characterized by a skeletonsize of 200 nm to 10 μm.
 20. A method in accordance with claim 19wherein said carbon monolith is characterized by a skeleton size of 400nm to 1 μm.
 21. A method in accordance with claim 13 wherein saidmacropores are of a size range of 0.05 μm to 100 μm.
 22. A method inaccordance with claim 21 wherein said macropores are of a size range of0.1 μm to 50 μm.
 23. A method in accordance with claim 22 wherein saidmacropores are of a size range of 0.8 μm to 10 μm.
 24. A method inaccordance with claim 13 wherein said mesopores are of a size range of18 Å to 50 nm.
 25. A method in accordance with claim 24 wherein saidmesopores are of a size range of 0.5 nm to 40 nm.
 26. A method inaccordance with claim 25 wherein said mesopores are of a size range of 5nm to 30 nm.